WO2017060105A1

WO2017060105A1 - Particle sensor for particle detection

Info

Publication number: WO2017060105A1
Application number: PCT/EP2016/072784
Authority: WO
Inventors: Michiel Johannes Jongerius; Koray Karakaya
Original assignee: Koninklijke Philips N.V.
Priority date: 2015-10-08
Filing date: 2016-09-26
Publication date: 2017-04-13

Abstract

The invention provides a particle sensor (100) for detecting particles, a related method (200), and a computer program product (300) comprising code to execute this method (200), where the particle sensor (100) comprises a light source (40), preferably a laser or an LED, adapted to create a focused illumination beam (50) passing the detection volume (20) to illuminate at least some of the particles (10, 11) within the detection volume (20), the light source (40) comprising a lens arrangement (44) for providing the illumination beam (50) with a focal area (54) around a focal point with an average diameter (54D) below the average particle distance of smaller particles (10) within the carrier medium (30) to enable detection of the smaller particles (10) within the particle size range when present inside the focal area (54), where the focal area (54) is axially movable along a propagation direction (55) of the illumination beam (50) enabling the detection of larger particles (11) within the particle size range at any position illuminated by the illumination beam (50) even outside the focal area (54), where a detection system (60) of the particle sensor (100) is adapted to detect intensity variations (61) of the transmitted, scattered, reflected or fluorescence light from at least one illumination beam (50) when the particles (10, 11) are illuminated.

Description

Particle sensor for particle detection

Field of the invention

The invention relates to a particle sensor for detecting particles, to a related method, and to a computer program product comprising code to execute this method. Background of the invention

Atmospheric particles are microscopic solid or liquid matter suspended in the Earth^'s atmosphere. Sources of particles can be man-made or natural. They have impacts on climate and precipitation that adversely affects human health, especially the concentration of fine particles (diameter of 2.5 μιτι or less, so-called PM2.5 particles) is very important parameter to monitor the air pollution. PM2.5 particles tend to penetrate into the gas exchange regions of the lung, leads to plaque deposits in arteries and therefore cause severe health problems. In order to determine the concentration of critical particles in air particle sensors are used to measure the level of pollution in the air. Low-cost systems are available based on the measurements of light scattered at the particle passing by with the air flowing through a detection volume in the sensor driven by a fan or a heater. These pulses are amplified, filtered and counted in an electronic system. US 6,677,573 B2 discloses such a particle sensor system comprising a laser light source, a condenser lens and a pin hole plate disposed adjacent to the condenser lens to provide a laser light beam having a constant diameter over a long section longer than 100 mm and a detection portion positioned face to face to the light beam passed the pin hole to be irrespective to small changes of the detection position of particles in order to achieve a stable detection. Optical sensors, for example the ones operating as PM2.5 detectors, need to provide response, preferably over the full size range of particles up to 2.5 μιτι, but practically between 0.2 μιτι - 2.5 μιτι range of particle sizes to collect the signals for generating reliable information on the total PM2.5 concentration. This means that the detection volume through which the particle containing air flow is passed should be small enough to be able to count the many smaller particles as individual pulses. At the same time a large detection volume is needed to capture a sufficient number of larger particles to obtain a low shot noise level in a given detector response time. Both are conflicting requirements.

There is a demand for a particle sensor being able to provide reliable signals with low shot noise over the full range of particle sizes within the scope of application; e.g. less than 2.5 μιτι in diameter for PM2.5 detection, less than 10 m in diameter for PM10 detection etc.

Summary of the invention

It is an object of the present invention to provide an improved particle sensor for particle density detection provide reliable signals with low shot noise over the full range of particle sizes being of interest. The invention is defined by the independent claims. The dependent claims define advantageous embodiments. According to a first embodiment a particle sensor for detecting particles within a predefined particle size range passing a detection volume of the particle sensor along a flow of a carrier medium. The particle sensor comprises a light source adapted to create at least one focused illumination beam passing the detection volume to illuminate at least some of the particles within the detection volume, the light source comprises at least one light source unit and a lens arrangement providing the illumination beam with a focal area around a focal point with an average diameter below the average particle distance of smaller particles within the carrier medium enabling detection of the smaller particles within the particle size range when present inside the focal area, where the focal area is movable along a propagation direction of the illumination beam enabling the detection of larger particles within the particle size range at any position illuminated by the illumination beam, where a detection system of the particle sensor is adapted to detect intensity variations in transmitted, scattered, reflected or fluorescence light from at least one illumination beam when the particles being illuminated.

The particle sensor according to the present invention provide options for relieving on conflicting requirements for the detection volume through which the particle containing air flow is passed on one hand to decrease the detection volume in size to be able to count the many smaller particles as individual pulses and on the other hand to enlarge the detection volume to capture a sufficient number of large particles to obtain a low shot noise level in a given detector response time by introducing a focal area being movable along the propagation direction of the illumination beam. The particle sensor according to the present invention provides a sufficiently small optical scattering volume denoted as the focal area having a certain diameter, where the light intensity is high enough to generate detectable intensity variation when smaller particles are passing through and when the required high light intensity is concentrated to a volume (focal area) being small enough to enable particle counting without overlapping particles, which is determined by the detection limit for smaller particles and simultaneously provides a sufficiently large optical scattering volume when moving the focal area along the propagation direction of the illumination beam for counting a sufficient number of particles at a reasonable sampling time, which is determined by the detection limit for the larger particles. The shape of the focal area depends on the shape of the illumination beam generated by the applied optics of the lens arrangement. As an example the focal area might be a spherical volume or an equipotential ellipsoid around the focal point. In case of volumes deviating from a spherical shape, the diameters may vary for different directions. In this case all different diameters result in an average diameter as specified above as the diameter. In order to collect a certain minimum number of detected larger particles, especially for larger particles of more than 2 μιτι diameter, it is beneficial to move the focal area along the illumination beam in order to "find" these larger particles at any position in the illumination beam in a shorter time to increase the number of detected particles within a time interval when moving the focal area (detection scan along the illumination beam). The movement of the focal area is an axial movement of the focal area in order to scan along the propagation of the direction beam to avoid double counting of particles. A non-axial movement partly parallel to the flow of the carrier medium could lead to double counting of the same particles. In an embodiment the light source is a laser, preferably a diode laser, or an LED. The detection volume to be passed by the carrier medium might be provided by open pipe comprising side walls made of a material being transparent for the illumination beams or the detection system and/or the light source are arranged inside the detection volume. The detection system may comprise multiple photonic sensors or a camera to spatially resolve and individually select the detection signals from the various areas illuminated separately by the illumination beams. Alternatively a single photo detector might be used to capture the whole illuminated area by the illumination beam and then filtering out the intensity variation in transmitted, scattered, reflected or fluorescence light from the illumination beam related to different particles in case of the light of the illumination beams having different properties such as different pulse schemes, different colors (wavelengths) or different polarizations or other differences, e.g. the smaller particles will create short pulses of the light intensity variation, whereas the larger particles will create much longer pulses of the light intensity variation when the particle passing the illumination beams. The terms "short" and "long" depends on the velocity of the particles, which is mainly determined by the velocity of the carrier medium carrying the particles within its flow, on the size of the particles and on the size of the areas illuminated by the illumination beam. However, the size of the areas illuminated by the illumination beams is determined by the applied the light source, the velocity of the carrier medium is predetermined by a corresponding flow generating module, e.g. a pump or a fan pumping or blowing the carrier medium through the detection volume of the particle sensor. The carrier medium might be a suitable gas or fluid, which particle density shall be measured and controlled. The detection system may detect the light intensity variations as light pulses being detected in direct, diffractive or reflective mode, where in the direct mode particles in the light path shield light from the detector resulting in an intensity drop as the light pulse, in diffractive mode light is measured that is scattered from the particles under an angle with respect to the illumination beam, while in the reflective mode particles scatter light from the illumination beam back towards the light source, e.g. a laser, resulting in a signal through self-mixing interference. In a preferred embodiment, the detection system is arranged outside the illumination beam and being operated in the diffractive or reflective mode to avoid the light of the original illumination beam propagating directly to the detector system to improve the signal- to-noise ration of the detected light intensity variations. The light pulses are

transferred into detection signals by the detection system. The shape of the light pulses is used to distinguish between particles having different sizes (diameters), especially between smaller and larger particles. In an embodiment the predefined particle size range ranges from particle diameters of 0.2 μιτι to particle diameters of 2.5 μιτι, which is commonly denotes as PM2.5. Depending on the application the particle sensor according to the present invention might be used also for other predefined particle size range, for example PM10, where the properties of the illumination beams, the detection volume and the light source are adapted accordingly. The term "smaller particles" denote the particles within a particle diameter close to the lower boundary of the particle size range (particles with diameters in the lower half of the particle size range), while the term "larger particles" denote the particles within a particle diameter close to the upper boundary of the particle size range (particles with diameters in the upper half of the particle size range).

The particle sensor may for example be used in order to detect or estimate air pollution. The particle sensor may alternatively be used in industrial applications in which an estimation of particle density may be relevant. The particle sensor may be a separate device or integrated in another device. The particle sensor may be used to indicating the particle concentration level in order to drive the operation of an air purifier device. The particle sensor may be used as part of an air purifier system for indoor, by optical light scattering. Alternatively to measurements of particles in air or other gases, the particle sensor according to the present inventions might be applied as particle sensor in fluids, e.g. processing fluids, water or blood.

The particle sensor provides options for relieving on the discussed conflict between demanded large and small detection volumes by introducing a motion of the illuminated focal area around the focus. In this way, a much larger volume of the carrier medium is scanned on the presence of the larger particles in the PM2.5 particles size range in order to collect sufficient number of these particles in a given measuring time frame to obtain sufficiently low shot noise level. With a moving focal area the number of detected larger particles is increased compared to the situation, when having an illumination beam with fixed non-moving focal area, while

maintaining a small focal area in order to keep being sensitive to smaller particles. Therefore the particle sensor according to the present invention provides an improved particle sensor for particle density detection providing reliable signals with low shot noise over the full range of particle sizes being of interest. In an embodiment the lens arrangement is adapted to provide a focal area, where the average diameter of the focal area is less than 1000 μιτι. In case of a spherical volume as the focal area the average diameter is the diameter of the sphere. In case of volumes deviating from a spherical shape, the diameters may vary for different directions. In this case all different diameters result in an average diameter as specified above. In case of a focal area with such a diameter an average number of only one particle of a size down to 300 nm is present at the same time within the focal area for particle concentrations below 35 g/m³. Up to this this concentration, the number of present particle down to sizes of 300nm can be individually counted. In a preferred embodiment the diameter of the focal area is less than 500 μιτι, where an average number of only one particle of a size down to 200 nm is present at the same time within the focal area for particle concentrations below 1 15 g/m³. Up to this concentration, the number of present particles down to sizes of 200nm can be detected with sufficient accuracy. In case of a focal area of a diameter of 200 μιτι, particles of sizes of 200 nm can be detected with sufficient accuracy up to a concentration of 500 g/m³.

In another embodiment the lens arrangement comprises a lens, which is mechanically movable along the propagation direction of the illumination beam in order to move the focal area. Applying such a mechanical solution to adjust the position of the focal area enables the use of any suitable lens, even lenses with a nominal focus length. Here the focal length of the focused beam is maintained while shifting the beam as such including the movement of the focal area. In another embodiment the lens arrangement comprises a lens with an adjustable focal length, preferably a fluid focus lens, in order to move the focal area. Such arrangement avoids mechanically moving parts to adjust the focus length. An electronically adjusted focus length can be controlled more easily and is

advantageous from the maintenance point of view. Since the focal area is the area around the focal point, a movement of the position of the focal point correspondingly to a varying focal length will also move the focal area.

In another embodiment the lens arrangement may comprises one or more lenses, where the mechanical movement of the one or more lenses will additionally result in a modified focal length. However, both effects result in a movement of the focal area.

In another embodiment the light source is adapted to provide multiple separate and non-overlapping illumination beams. The number of beams improves the number of detected particles, where the shot noise level especially for larger particles can be improved significantly. If multiple illumination beams are present, the moving speed of the focal area along the propagation direction of the illumination beam could be slower in order to achieve the same good shot noise level compared to the

embodiment of the particle sensor only applying one illumination beam. The focal areas of each illumination beam might be moved simultaneously, preferably the focal areas of each illumination beam might be moved independently.

In another embodiment the light source comprises one single light source providing an initial beam illuminating the lens arrangement, where the lens

arrangement is adapted to separate the initial beam into the multiple illumination beams. In this embodiment only one light source, e.g. a diode laser as the light source, has to be operated providing one or more illumination beams. The term

"initial beam" denotes the part of the beam between light source and the lens or the lenses. The shape of the initial beam depends on the particular application and the lens arrangement.

In an alternative embodiment the light source comprises multiple light sources each providing a separate initial beam and individual lens arrangements each illuminated by the separate initial beams in order to provide the multiple separate illumination beams. In this embodiment the light sources could be operated differently, e.g. apply different illumination beam properties for receiving more detailed data, not only a light intensity variation. The focal length of the different illumination beams might be adjusted differently. Also the scheme of moving the focal area along the propagation direction of the illumination beams might be different for different illumination beams.

The light source may comprise a laser or LED array as the multiple light source units for providing individual illumination beams. The laser or LED array may comprise at least the first laser or LED and a second laser or LED. The particle sensor may further comprise a controller. The lasers or LEDs may be adapted to enable independent detection of the particle. The controller may be adapted to reduce multiple counts of the particle. The reduction of multiple counts of the particle may be done by means of a theoretical model of particle movement stored, for example, in the controller. The theoretical model may enable to determine

coincidences of detection of one particle by means of a first and a second

illumination beam having a corresponding beam shape.

The lens arrangement may, for example, be a lens array or array of micro- lenses. An array of micro-lenses may, for example, be used if the laser array comprises a single chip of semiconductor lasers. The semiconductor lasers may, for example, be Vertical Cavity Surface Emitting Lasers (VCSEL).

In another embodiment the multiple illumination beams each comprise a central axis through the focal point arranged in a predefined angle to the flow of the carrier medium within the detection volume and wherein the detection system is adapted to determine a particle velocity within the carrier medium for larger particles within the particle size range from the detection signals caused by one particle passing at least two illumination beams with a corresponding time difference. In a preferred embodiment the central axes are arranged perpendicular to the flow of the carrier medium. The determined particle velocities within the carrier medium can be used to monitor differences/ drifts in the speed of the carrier medium and to adapt the calibration of the detection system for potential differences of the speed of the carrier medium, e.g. drifts in pump, fan or buoyancy speeds. In another embodiment at least two illumination beams having different colors and/or at least one of the illumination beams is a polarized light beam. In a preferred embodiment multiple illumination beams are polarized light beams, more preferably all polarized light beams being polarized differently. In a further preferred

embodiment all illumination beams have different colors. In another embodiment at least two illumination beams having different colors and/or at least one of the illumination beams is a polarized light beam. In order to provide polarized light beams, the light source comprises polarization filters arranged within the initial beam generated by the light source unit(s) or arranged within the illumination beam(s). The polarization filters might by switchable polarization filters. The different colors of the illumination beam(s) might be achieved by arranging suitable color filters into the illumination beam(s) in case of the light source emitting light spread over of a certain wavelengths interval, e.g. white light. Alternatively one or more (or all) light source units may emit light at different wavelength providing illumination beams having different colors.

The polarized light and/or the colored light may provide additional information about the nature of the particles and hence a more accurate PM2.5 determination.

In another embodiment the light source provides at least one pulsed

illumination beam. The pulsed illumination beam(s) enable to measure time dependent signals. This can be done in one illumination beam only not compromising any of the other features of the particle sensor according to the invention. In another embodiment at least two illumination beams, preferably all illumination beams, are pulsed beams. Pulsed illumination beams give additional information about the nature of the detected particles, e.g. whether they are of biological nature.

In an embodiment the detection system comprises a set of multiple light detectors suitably arranged and adapted to measure the intensity variations of transmitted, scattered, reflected or fluorescence light caused by the particles individually for each illumination beam.

Here the detection system may comprise multiple photo detectors, detector array or a camera with a suitable number of pixels providing a suitable resolution to spatially resolve and individually select the detection signals from the various areas illuminated separately by the illumination beams. Alternatively a single photo detector might be used to capture the whole illuminated area by all illumination beams and then filtering out the separated illuminated areas for each illumination beam in case of the light of the illumination beams having different properties such as different pulse schemes, different colors (wavelengths) or different polarizations or other differences. The smaller particles will create short pulses of the intensity variation and larger particles will create much longer pulses of the intensity variation as detection signals. So these size classes can be distinguished in the detector system by binning the intensity variations due to light scattered by the particles on the length of the intensity variations (pulse length). A device like a mobile communication device (laptop, smart phone, PAD and the like) may comprise a particle sensor as described above.

According to a further embodiment a method for detecting particles within a predefined particle size range passing a detection volume of a particle sensor according to the present invention along a flow of a carrier medium is presented. The method comprises the steps of:

creating at least one illumination beam for passing the detection volume by a light source of the particle sensor comprising at least one light source unit and a lens arrangement providing the illumination beam and enabling a focal area around a focal point being movable along the propagation direction of the illumination beam; focusing the illumination beam by the lens arrangement to provide the focal area with an average diameter below the average particle distance of smaller particles of the particle size range;

- illuminating at least some of the particles within the detection volume by the illumination beam;

detecting the smaller particles within the particle size range inside the focal area with the illumination beam;

detecting the larger particles within the particle size range at any position illuminated by the illumination beam by moving the focal area along the propagation direction of the illumination beam; and

providing detection signals of the detection of smaller and larger particles by the detection system based on intensity variations of transmitted, scattered, reflected or fluorescence light from the illumination beam when particles being illuminated.

The steps of the method are not necessarily performed in the order as presented above. Especially both detection steps might be executed simultaneously or in a reversed sequence. For smaller particle detection there is no need to move the focal area in order to detect the small particles accurately with a low shot noise, while for detection of the larger particle a moving focal area is required in order to increase the number of detected particles to achieve a low shot noise. However when moving the focal area, also small particles might be detected.

In an embodiment the method comprises the additional step of providing multiple separate and non-overlapping illumination beams. In a preferred embodiment in case of multiple illumination beams the method comprises the additional step of determining a particle velocity within the carrier medium for larger particles within the particle size range from the detection signals caused by one particle passing at least two illumination beams with a corresponding time difference, where the multiple illumination beams having central axes through the focal point arranged parallel to each other and in a predefined angle, preferably perpendicular, to the flow of the carrier medium within the detection volume.

In another embodiment the method comprises the additional step of

measuring the intensity variations caused by the particles individually for each detected particle by the detection system comprising a set of multiple light detectors being suitably arranged.

In another embodiment the method comprises the additional step of increasing the number of illumination beams in order to reduce a noise level for a particular particle size below a predefined threshold. In order to obtain a low shot noise level in a given detector, the capture of a sufficient number of particles is necessary.

Especially for the larger particles, an even larger volume, where particles can be detected might be advantageous. Therefore particle sensors providing a higher number of illumination beams will result in a higher number of detected larger particles and therefore in a reduced shot noise level and in a better accuracy of the measurement results. As an example for detecting a concentration of 35 pg/m³for larger particles at least 100 of these particles have to be measures in the detector response time to have a shot noise level less than 10%.

According to a further embodiment a computer program product is presented. The computer program product comprises code which can be saved on at least one memory device comprised by the particle sensor according to any one of claims 1 to 1 1 or on at least one memory device of a device comprising the particle sensor according to any one of claims 1 to 1 1 , wherein the code is arranged such that the method according to any one of claims 12 to 14 can be executed by means of at least one processing device comprised by the particle sensor according to any one of claims 1 to 1 1 or by means of at least one processing device of the device

comprising the particle sensor. The memory device or the processing device may be comprised by the electrical driver and/or the controller and/or the device comprising the particle sensor. A memory device and/or processing device of the device comprising the particle sensor may interact with a memory device and/or processing device comprised by the particle sensor.

It shall be understood that the particle sensor according to any one of claims 1 to 1 1 and the method of any of claims 12 to 14 have similar and/or identical embodiments, in particular, as defined in the dependent claims.

It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims with the respective independent claim.

Further advantageous embodiments are defined below. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. Brief description of the drawings

The invention will now be described, by way of example, based on

embodiments with reference to the accompanying drawings.

In the drawings:

Fig. 1 shows a principal sketch of an embodiment of the particle sensor according to the present invention.

Fig. 2 shows a principal sketch of an embodiment of the light source of the particle sensor according to the present invention.

Fig. 3 shows a principal sketch of another embodiment of the light source of the particle sensor according to the present invention.

Fig. 4 shows a principal sketch of another embodiment of the particle sensor according to the present invention.

Fig. 5 shows a principal sketch of another embodiment of the light source of the particle sensor according to the present invention.

Fig. 6 shows a principal sketch of an embodiment of the detection system of the particle sensor according to the present invention

Fig. 7 shows a principal sketch of an embodiment of a computer program product comprising code for saving on the particle sensor according to the present invention. Fig. 8 shows a principal sketch of an embodiment of a computer program product comprising code for saving on a device comprising the particle sensor according to the present invention.

Fig. 9 shows a principal sketch of an embodiment of a method for detecting particles using the particle sensor device according to the present invention.

In the Figures, like numbers refer to like objects throughout. Objects in the Figures are not necessarily drawn to scale. Detailed description of embodiments

Fig. 1 shows a principal sketch of an embodiment of the particle sensor 100 according to the present invention. The particle sensor 100 comprises a light source 40 adapted to create a focused illumination beam 50 passing the detection volume 20 to illuminate at least some of the particles 10, 1 1 within the detection volume 20. Here the light source 40 comprises one light source unit 41 and a suitable lens arrangement 44 providing the illumination beam 50 with focal area 54 around a focal point with an average diameter 54D below the average particle distance of smaller particles 10 within the carrier medium 30 enabling the detection of the smaller particles 10 within the particle size range when present inside the focal area 54, as indicated by the black circle (see also Fig. 2 - 4 in addition). The smaller particles 10 do not have to exactly pass the focal point. For a reliable detection of the smaller particle 10, they only have to pass the focal area 54 in order to provide a sufficient light intensity variation being measured by the detection system 60. Simultaneously the focal area 54 is movable 57 along a propagation direction 55 of the illumination beam 50 enabling the detection of larger particles 1 1 within the particle size range in parallel at any position illuminated by the illumination beam 50. The detection system 60 of the particle sensor 100 is adapted to detect intensity variations of the at least one illumination beam 50 as detection signals 61 when the particles 10, 1 1 being illuminated. The detection system 60 might comprises a photodiode in order to measure the light intensity variation, which could be detected in a direct mode by shielding the light of the illumination beam resulting in a drop of the light intensity corresponding to the detected particle transferred into the detection signals 61 or could be detected in a reflective mode by scattering the light of the illumination beam resulting in an increase of the light intensity corresponding to the detected particle transferred into the detection signals 61 . In the direct mode the detection system 60 is arranged inline face-to-face with the propagation direction of the illumination beam 50 as shown here. In an alternative embodiment the detection system 60 might be used in a diffractive mode, where the detector system 60 of Fig .1 might be arranged outside the illumination beam 50, e.g. in a 90° angle to the propagation direction of the illumination beam 50, to only collect the light that is scattered under an angle from the particles (not shown here) and not the light of the original illumination beam 50. In a further embodiment the detector system might be used in a reflective mode, where the scattered light is propagating back into the laser as the light source 41 creating a signal, e.g. by self-mixing interference (not shown here).

If a particle 10, 1 1 is located within the focal area 54 (dashed area) the light is either shielded or scattered, where the light intensity variation is sufficiently large so that it can be detected by the detection system 60. In general, a flow of the carrier medium, e.g. air, is applied driving the particles 10, 1 1 to pass through the detection volume 20 and eventually to pass through the focal area 54. In order to enable counting individual particles 10,1 1 coexistence of more than one particle 10, 1 1 in the focal area 54 should be avoided. The average distance between two particles is a function of the PM2.5 concentration and the particle size within the PM2.5 particle size range. For smaller particles 10 down to 200nm diameter the distance between two of these particles is typically 400 μιτι at a PM2.5 concentration of 1 15 g/m3. This distance is however much greater for larger particles 1 1 in the carrier gas, e.g. air. For instance, particles with a diameter of 2000 nm diameter the distance between two of these particles is typically 6 mm at a PM2.5 concentration of 35 g/m3.

Therefore the lens arrangement 44 is adapted to provide a focal area 54, where the diameter 54D is less than 1000 μιτι, preferably less than 500 μιτι.

Fig. 2 shows a principal sketch of an embodiment of the light source 40 of the particle sensor 100 according to the present invention, where the lens arrangement 44 comprises a lens 45, which is mechanically movable (indicated by the horizontal arrow inside the lens arrangement 44) along the propagation direction 55 of the illumination beam 50 in order to move the focal area 54 with an (average) diameter 54D. Here the initial light beam created by the light source unit 41 enters the movable lens 45 as an essentially parallel light beam, e.g. by placing a collimating lens into the initial light beam between light source unit 41 and the movable lens 45. The dashed lens 45 with a certain constant focal length 53 provides a illumination beam 50 with a focal point closer to the light source 40 and the corresponding focal area 54 around this focal point at a first position of the lens 45 closer to the light source unit 41 (dashed lines). When moving the movable lens 45 from the first position to a second position with larger distance to the light source unit 41 , the focal point and the corresponding focal area 54 move correspondingly to a position with a larger distance to the light source 40 (closed lines). In both cases the focal length 53 stays the same. Applying such a mechanical solution to adjust the position of the focal area 54 enables the use of any suitable lens, even lenses with a nominal focus length. In an alternative embodiment of the lens arrangement 44 not shown here the initial light beam originating from the light source 41 may enter the movable lens 45 directly as a non-collimated light beam, where moving the lens 45 towards the light source 41 will results in a focal area 54 being further shifted away from the light source 40 and vice versa.

Fig. 3 shows a principal sketch of another embodiment of the light source 40 of the particle sensor 100 according to the present invention, where the lens arrangement 44 comprises a lens 46 with an adjustable focal length 53 in order to move the focal area 54, preferably a fluid focus lens 46. Here the position of the lens 46 inside the lens arrangement 44 is constant, but the focal length 53 can be varied between a first focal length 53 resulting in a smaller distance between focal point and therefore the focal area 54 around the focal point to the light source 40 and a second focal length 53 resulting in a larger distance between focal point and therefore the focal area 54 around the focal point to the light source 40. The difference between possible first and second local lengths 53 at least depends on the lenses 46 used within the lens arrangement 44. Applying suitable lenses 45, 46, the embodiments shown in Fig.2 and 3 might be also combined to enlarge the range of possible positions of the focal area 54.

Fig. 4 shows a principal sketch of another embodiment of the particle sensor 100 according to the present invention, wherein the light source 40 provides three separate and non-overlapping illumination beams 50, 51 , 52. In this embodiment the light source 40 comprises one single light source unit 41 providing a diverging initial beam illuminating the lens arrangement 44, where the lens arrangement 44 is adapted to separate the initial beam into the multiple illumination beams 50, 51 , 52. In other embodiments the light source 40 may comprise multiple light source units 41 , 42, 43 each providing a separate initial beam and individual lens arrangements 44 each illuminated by the separate initial beams in order to provide the multiple separate illumination beams 50, 51 , 52. The three illumination beams 50, 51 , 52 further have central axes 56 through the focal point, which arranged parallel to each other and perpendicular to the flow of the carrier medium 30 within the detection volume 20 in this embodiment. In this case the detection system 60 is able to determine a particle velocity within the carrier medium 30 for larger particles 1 1 within the particle size range from the detection signals 61 caused by one particle 1 1 passing at least two illumination beams 50, 51 , 52 with a corresponding time difference. Here a smaller particle 10 is detected inside the focal area 54 of upper illumination beam 52. For detecting the small particles 10, the particles 10 have to be inside the focal area 54 in order to provide a sufficient detectable interaction with the illumination beam 52. However the number of small particles 10 is sufficiently large enabling to achieve a low shot noise even when not moving the focal area 54. In contrast to that the number of present larger particles 1 1 requires to move the focal area 54 along the propagation direction of the illumination beam 50.The larger particle 1 1 will be detected simultaneously with the lower illumination beam 50 when moving the focal area 54 accordingly. In another embodiment the light source 40 may provide pulsed illumination beams 50, 51 , 52. The pulsed illumination beams 50, 51 , 52 enables measuring of time dependent signals. Pulsed illumination beams 50, 51 , 52 may also give additional information about the nature of the detected particles, e.g. whether they are of biological nature.

The light source 40 may also comprise an array of light source units 41 , 42, 43, e.g. a laser array 41 , 42, 43, for providing individual illumination beams 50, 51 , 52. The particle sensor 100 may further comprise a controller (not shown here). The light source units 41 , 42, 43 may be adapted to enable independent detection of the particle 10, 1 1 . The controller may be adapted to reduce multiple counts of the particle 10, 1 1 . The reduction of multiple counts of the particles 10, 1 1 may be done by means of a theoretical model of particle movement stored, for example, in the controller. The theoretical model may enable to determine coincidences of detection of one particle 10, 1 1 by means of the illumination beams 50, 51 , 52 having the beam shape as shown in Fig .1 . Fig. 5 shows a principal sketch of another embodiment of the light source 40 of the particle sensor 100 according to the present invention as shown in Fig.4, where polarizing filters 47 and color filters 48 are arranged within the illumination beams 50, 51 , 52 generated by the light source 40. The polarization and color filters 47, 48 might be separated in three corresponding filters each arranged within the individual illumination beams 50, 51 , 52 separately from the neighbored illumination beams 50, 51 , 52. This enables that at least two illumination beams 50, 51 , 52 having different colors and/or at least one of the illumination beams 50, 51 , 52 is a polarized light beam. In a preferred embodiment all three illumination beams 50, 51 , 52 are polarized light beams. In case of individual and separately arranged and controlled polarization filters 47 all polarized light beams 50, 51 , 52 might be polarized differently. The same holds for individual and separately arranged and controlled color filters 48 enabling all illumination beams 50, 51 , 52 having different colors. The polarized light 50, 51 , 52 and/or the colored light 50, 51 , 52 may provide additional information about the nature of the particles 10, 1 1 and hence a more accurate PM2.5 determination.

Fig. 6 shows a principal sketch of an embodiment of the detection system 60 of the particle sensor 100 according to the present invention with multiple illumination beams 50, 51 , 52, where the detection system 60 comprises a set of multiple light detectors 62 suitably arranged and adapted to measure the intensity variations caused by the particles 10, 1 1 individually for each detected particle 10, 1 1 . Here the detection system 60 may comprise multiple photo detectors 62, a detector array 62 or a camera with a suitable number of pixels 62 providing a suitable resolution to spatially resolve and individually select the detection signals 61 from the various areas illuminated separately by the illumination beams 50, 51 , 52. The smaller particles 10 will create short pulses of the intensity variation and larger particles 1 1 will create much longer pulses of the intensity variation as detection signals 61 . In an alternative embodiment the detection system 60 as shown in Fig.6 might be used in a diffractive mode, where this detector system 60 might be arranged outside the illumination beam 50, e.g. in a 90° angle to the propagation direction of the

illumination beam 50, to only collect the light that is scattered under an angle from the particles (not shown here) and not the light of the original illumination beam 50. In a further embodiment the detector system might be used in a reflective mode, where the scattered light is propagating back into the laser as the light source 41 creating a signal, e.g. by self-mixing interference (not shown here).

Fig. 7 shows a principal sketch of an embodiment of a computer program product 300 comprising code 310 for saving on the particle sensor 100 according to the present invention. The computer program product 300 comprises code 310 which can be saved on at least one memory device comprised by the particle sensor 100 according to the present invention, wherein the code means being arranged such that the method according to the present invention can be executed by means of at least one processing device comprised by the particle sensor 100 according to the present invention. Fig. 8 shows a principal sketch of an alternative embodiment to the embodiment shown in Fig.7, where a computer program product 300 comprising code 310 is intended for saving on a device 400 comprising the particle sensor 100 according to the present invention. The computer program product 300 comprises code 310 which can be saved on at least one memory device 70 comprised by the particle sensor 100 or on at least one memory device 410 of a device 400 comprising the particle sensor 100, wherein the code 310 is arranged such that the method according to the present inventions (see also Fig.9) can be executed by means of at least one processing device 80 comprised by the particle sensor 100 or by means of at least one processing device 420 of the device 400 comprising the particle sensor 100. The device 400 might be a mobile communication device (laptop, smart phone, PAD and the like) comprising the particle sensor 100 as described above.

Fig. 9 shows a principal sketch of a method for detecting particles using the particle sensor 100 according to the present invention. The method comprises the steps of creating 210 at least one focused illumination beam 50 for passing the detection volume 20 by a light source 40 of the particle sensor 100 comprising at least one light source unit 41 and a suitable lens arrangement 44 providing the illumination beam 50 and enabling a focal area 54 around a focal point being movable 57 along the propagation direction 55 of the illumination beam 50; focusing 220 the illumination beam 50 by the lens arrangement 44 to provide the focal area 54 with an average diameter 54D below the average particle distance of smaller particles 10 of the particle size range; illuminating 230 at least some of the particles 10, 1 1 within the detection volume 20 by the illumination beam 50; detecting 240 the smaller particles 10 within the particle size range inside the focal area 54 with the illumination beam 50; detecting 250 the larger particles 1 1 within the particle size range at any position illuminated by the illumination beam 50 by moving 57 the focal area 54 along the propagation direction 55 of the illumination beam 50; and providing 260 detection signals 61 of the detection of smaller and larger particles 10, 1 1 by the detection system 60 based on intensity variations of the illumination beam 50 when particles 10, 1 1 being illuminated.

In an embodiment the method may comprise the additional steps (dashed method steps) of creating 21 1 multiple illumination beams 51 , 52 by the light source 40, and determining 270 a particle velocity within the carrier medium 30 for larger particles 1 1 within the particle size range from the detection signals 61 caused by one particle 1 1 passing at least two of the multiple illumination beams 50, 51 , 52 with a corresponding time difference, where the illumination beams 50, 51 , 52 having central axes 56 through the focal point arranged parallel to each other and

perpendicular to the flow of the carrier medium 30 within the detection volume 20.

In another embodiment the method comprises the additional step (dashed method step) of measuring 280 the intensity variations caused by the particles 10, 1 1 individually for each detected particle 10, 1 1 by the detection system 60 comprising a set of multiple light detectors 62 being suitably arranged.

The steps of the method are not necessarily performed in the order as presented in Fig.8.

While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the art and which may be used instead of or in addition to features already described herein. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality of elements or steps. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

List of reference numerals:

10 particles (smaller particles)

1 1 particles (larger particles)

20 detection volume

30 carrier medium, flow of the carrier medium

40 light source

41 light source unit of the light source

42, 43 further light source units

44 lens arrangement

45 movable focal lens

46 focus lens with adaptable focal length

47 polarizing filter

48 color filter

50 illumination beam

51 , 52 further illumination beams

53 focal length of the illumination beam(s)

54 focal area around the focal point

55 propagation direction of the illumination beam

56 central axis of the illumination beams

60 detection system

61 detection signals

62 multiple light detectors of the detection system

70 memory device of the particle sensor

80 processing device of the particle sensor

100 particle sensor

200 method of particle detection

210 creating the illumination beam

21 1 creating additional separate non-overlapping illumination beams

220 focusing the at least one illumination beam(s)

230 illuminating at least some of the particles

240 detecting the smaller particles 250 detecting the larger particles

260 providing detection signals of the detection of particles

270 deternnining the velocity of larger particles within the carrier medium

280 measuring the intensity variations caused by the particles individually

300 computer program product

310 code of the computer program product

400 device comprising the particle sensor

410 memory device of the device 400

420 processing device of the device 400

Claims

1 . A particle sensor (100) for detecting smaller particles (10) and larger particles (1 1 ) within a predefined particle size range passing a detection volume (20) of the particle sensor (100) along a flow of a carrier medium (30), the smaller particles (10) having diameters in the lower half of the particle size range and the larger particles (1 1 ) having diameters in the upper half of the particle size range, the particle sensor (100) comprising:

a light source (40) adapted to create a focused illumination beam (50) passing the detection volume (20) to illuminate at least some of the particles (10, 1 1 ) within the detection volume (20), the light source (40) comprising a lens arrangement (44) for providing the focused illumination beam (50) with a focal area (54) around a focal point, and

a detection system (60) adapted to detect intensity variations in transmitted, scattered, reflected or fluorescence light from the focused illumination beam (50) when the particles (10, 1 1 ) are illuminated;

characterized in:

the focal area (54) is provided to enable detection of the smaller particles (10) when present inside the focal area (54), and the focal area (54) is movable (57) along a propagation direction (55) of the focused illumination beam (50) to enable the detection of the larger particles (1 1 ) at any position illuminated by the focused illumination beam (50).

2. The particle sensor (100) according to claim 1 , wherein the lens arrangement (44) is adapted to provide a focal area (54), where the diameter (54D) of the focal area (54) is less than 1000 μιτι, preferably less than 500 μιτι.

3. The particle sensor (100) according to one of the preceding claims, wherein the lens arrangement (44) comprises a lens (45), which is mechanically movable along the propagation direction (55) of the focused illumination beam (50) in order to move the focal area (54).

4. The particle sensor (100) according to one of the preceding claims 1 or 2, wherein the lens arrangement (44) comprises a lens (46) with an adjustable focal length (53) in order to move the focal area (54), preferably a fluid focus lens (46).

5. The particle sensor (100) according to one of the preceding claims, wherein the light source (40) is adapted to provide multiple separate and non-overlapping illumination beams (50, 51 , 52).

6. The particle sensor (100) according to claim 5, wherein the light source (40) comprises one single light source unit (41 ) for providing an initial beam

illuminating the lens arrangement (44), where the lens arrangement (44) is adapted to separate the initial beam into the multiple illumination beams (50, 51 , 52).

7. The particle sensor (100) according to claim 5, wherein the light source (40) comprises multiple light source units (41 , 42, 43) each providing a separate initial beam and individual lens arrangements (44) each illuminated by the separate initial beams in order to provide the multiple separate illumination beams (50, 51 , 52).

8. The particle sensor (100) according to any of claims 5 to 7, wherein the multiple illumination beams (50, 51 , 52) having central axes (56) through the focal point arranged parallel to each other and in a predefined angle to the flow of the carrier medium (30) within the detection volume (20) and wherein the detection system (60) is adapted to determine a particle velocity within the carrier medium (30) for larger particles (1 1 ) within the particle size range from the detection signals (61 ) caused by one particle (1 1 ) passing at least two illumination beams (50, 51 , 52) with a corresponding time difference.

9. The particle sensor (100) according to any of claims 5 to 8, wherein at least two illumination beams (50, 51 , 52) having different colors and/or at least one of the illumination beams (50, 51 , 52) is a polarized light beam, preferably multiple illumination beams (50, 51 , 52) are polarized light beams, more preferably all polarized light beams (50, 51 , 52) being polarized differently or all illumination beams (50, 51 , 52) having different colors.

10. The particle sensor (100) according to one of the preceding claims, wherein the light source (40) is adapted to provide at least one pulsed illumination beam (50).

1 1 . The particle sensor (100) according to one of the preceding claims, wherein the detection system (60) comprises a set of multiple light detectors (62) suitably arranged and adapted to measure the intensity variations of transmitted, scattered, reflected or fluorescence light caused by the particles (10, 1 1 ) individually for each illumination beam (50, 51 , 52).

12. A method (200) for detecting smaller and larger particles within a predefined particle size range passing a detection volume (20) along a flow of a carrier medium (30), the smaller particles having diameters in the lower half of the particle size range and the larger particles having diameters in the upper half of the particle size range, the method comprising the steps of:

- creating (210) a focused illumination beam (50) for passing the detection volume (20), the focused illumination beam (50) having a focal area (54) around a focal point of the focused illumination beam (50), the focal area (54) having an average diameter (54D) below an average particle distance of the smaller particles

(10) of the particle size range, the focal area (54) being movable (57) along the propagation direction (55) of the focused illumination beam (50);

illuminating (230) at least some of the smaller particles (10) and larger particles

(1 1 ) within the detection volume (20) by the illumination beam (50); and

providing (260) detection signals (61 ) of the detection of smaller and larger particles (10, 1 1 ) by the detection system (60) based on intensity variations of transmitted, scattered, reflected or fluorescence light from the illumination beam (50) when particles (10, 1 1 ) being illuminated;

characterized in:

illuminating (240) the smaller particles (10) within the particle size range inside the focal area (54) with the illumination beam (50) to enable detection of the smaller particles (10);

illuminating (250) the larger particles (1 1 ) within the particle size range at any position illuminated by the illumination beam (50) by moving (57) the focal area (54) along the propagation direction (55) of the illumination beam (50) to enable detection of the larger particles (1 1 ).

13. The method according to claim 12, comprising the additional step of providing multiple separate and non-overlapping illumination beams (50, 51 , 52).

14. The method according to claim 13, comprising the additional step of determining (270) a particle velocity within the carrier medium (30) for larger particles (1 1 ) within the particle size range from the detection signals (61 ) caused by one particle (1 1 ) passing at least two illumination beams (50, 51 ) with a corresponding time difference, where the multiple illumination beams (50, 51 , 52) have central axes (56) through the focal point arranged parallel to each other and in a predefined angle to the flow of the carrier medium (30) within the detection volume (20).

15. A computer program product (300) comprising code (310) to enable execution of the method according to any one of claims 12 to 14 by means of at least one processing device (80, 420).